Google Search, commonly referred to as Google Web Search or just Google, is a web search engine owned by Google Inc. It is the most-used search engine on the World Wide Web,[4] handling more than three billion searches each day.[5][6] As of February 2015[update] it is the most used search engine in the US with 64.5% market share.[7]

The order of search on Google's search-results pages is based, in part, on a priority rank called a "PageRank". Google Search provides many different options for customized search, using Boolean operators such as: exclusion ("-xx"), alternatives ("xx OR yy OR zz"), and wildcards ("Winston * Churchill" returns "Winston Churchill", "Winston Spencer Churchill", etc.)[8] The same and other options can be specified in a different way on an Advanced Search page.

The main purpose of Google Search is to hunt for text in publicly accessible documents offered by web servers, as opposed to other data, such as images or data contained in databases. It was originally developed by Larry Page and Sergey Brin in 1997.[9] Google Search provides several features beyond searching for words.[10] These include synonyms, weather forecasts, time zones, stock quotes, maps, earthquake data, movie showtimes, airports, home listings, and sports scores. There are special features for numbers, dates, and some specific forms, including ranges,[11] prices, temperatures, money and measurement unit conversions, calculations, package tracking, patents, area codes,[10] and language translation. In June 2011 Google introduced "Google Voice Search" to search for spoken, rather than typed, words.[12] In May 2012 Google introduced a Knowledge Graphsemantic search feature in the U.S.

Analysis of the frequency of search terms may indicate economic, social and health trends.[13] Data about the frequency of use of search terms on Google have been shown to correlate with flu outbreaks and unemployment levels, and provide the information faster than traditional reporting methods and surveys.

Google's rise to success was in large part due to a patented algorithm called PageRank that helps rank web pages that match a given search string.[15] When Google was a Stanford research project, it was nicknamed BackRub because the technology checks backlinks to determine a site's importance. Previous keyword-based methods of ranking search results, used by many search engines that were once more popular than Google, would rank pages by how often the search terms occurred in the page, or how strongly associated the search terms were within each resulting page. The PageRank algorithm instead analyzes human-generated links assuming that web pages linked from many important pages are themselves likely to be important. The algorithm computes a recursive score for pages, based on the weighted sum of the PageRanks of the pages linking to them. PageRank is thought to correlate well with human concepts of importance. In addition to PageRank, Google, over the years, has added many other secret criteria for determining the ranking of pages on result lists, reported to be over 250 different indicators,[16][17] the specifics of which are kept secret to keep spammers at bay and help Google maintain an edge over its competitors globally.

In a potential hint of Google's future direction for their Search algorithm, Eric Schmidt, Google's then chief executive, said in a 2007 interview with the Financial Times: "The goal is to enable Google users to be able to ask the question such as 'What shall I do tomorrow?' and 'What job shall I take?'".[18] Schmidt reaffirmed this during a 2010 interview with the Wall Street Journal: "I actually think most people don't want Google to answer their questions, they want Google to tell them what they should be doing next."[19]

In 2013 the European Commission found that Google Search favored Google's own products, instead of offering consumers the best result for their needs.[20] In February 2015 Google announced a major change to its mobile search algorithm which would favor mobile friendly over other websites. Nearly 60% of Google's online search traffic comes from mobile phones. Google wants its users to have access to premium quality websites. Those websites which lack a mobile friendly interface would be demoted and it is expected that this update will cause a massive shake-up of ranks. Business who fail to update their websites accordingly could see a massive dip in their regular websites traffic.[21]

The exact percentage of the total of web pages that Google indexes is not known, as it is very difficult to accurately calculate. Google presents a two-line summary and also a preview of each search result, which includes a link to a cached (stored), usually older version of the page.

Google's cache link in its search results provides a way of retrieving information from websites that have recently gone down and a way of retrieving data more quickly than by clicking the direct link. This feature is still available, but many users are not aware of this because it has been moved to the previews of the search results presented next to these.[22][23]

Google not only indexes and caches web pages, but also takes "snapshots" of other file types, which include PDF, Word documents, Excel spreadsheets, Flash SWF, plain text files, and so on.[24] Except in the case of text and SWF files, the cached version is a conversion to (X)HTML, allowing those without the corresponding viewer application to read the file. Users can customize the search engine, by setting a default language, using the "SafeSearch" filtering technology and set the number of results shown on each page. Google has been criticized for placing long-term cookies on users' machines to store these preferences, a tactic which also enables them to track a user's search terms and retain the data for more than a year.[citation needed] For any query, up to the first 1000 results can be shown with a maximum of 100 displayed per page. The ability to specify the number of results is available only if "Instant Search" is not enabled. If "Instant Search" is enabled, only 10 results are displayed, regardless of this setting.[original research?]

In 2012, Google changed its rankings to demote sites that had been accused of piracy, except the Google-owned YouTube site.[25]

Despite its immense index, there is also a considerable amount of data available in online databases which are accessible by means of queries but not by links. This so-called invisible or deep Web is minimally covered by Google and other search engines.[26] The deep Web contains library catalogs, official legislative documents of governments, phone books, and other content which is dynamically prepared to respond to a query.

Because Google is the most popular search engine, many webmasters have become eager to influence their website's Google rankings. An industry of consultants has arisen to help websites increase their rankings on Google and on other search engines. This field, called search engine optimization, attempts to discern patterns in search engine listings, and then develop a methodology for improving rankings to draw more searchers to their client's sites. Search engine optimization encompasses both "on page" factors (like body copy, title elements, H1 heading elements and image alt attribute values) and Off Page Optimization factors (like anchor text and PageRank). The general idea is to affect Google's relevance algorithm by incorporating the keywords being targeted in various places "on page", in particular the title element and the body copy (note: the higher up in the page, presumably the better its keyword prominence and thus the ranking). Too many occurrences of the keyword, however, cause the page to look suspect to Google's spam checking algorithms. Google has published guidelines for website owners who would like to raise their rankings when using legitimate optimization consultants.[27] It has been hypothesized, and, allegedly, is the opinion of the owner of one business about which there have been numerous complaints, that negative publicity, for example, numerous consumer complaints, may serve as well to elevate page rank on Google Search as favorable comments.[28] The particular problem addressed in The New York Times article, which involved DecorMyEyes, was addressed shortly thereafter by an undisclosed fix in the Google algorithm. According to Google, it was not the frequently published consumer complaints about DecorMyEyes which resulted in the high ranking but mentions on news websites of events which affected the firm such as legal actions against it. Google Webmaster Tools helps to check for websites that use duplicate or copyright content.[29]

Universal search was launched by Google on May 16, 2007. It was an idea which merged the results from different searches into one. Prior to Universal search, a standard Google search would consist of links to different websites. Universal search incorporates a wide variety of information such as websites, news, pictures, maps, blogs, videos, and more to display as search results. Marissa Mayer, VP of Search Products & User Experience during Universal search launch, described the goal of universal search, "With Universal search, we're attempting to break down the walls that traditionally separated our various search properties and integrate the vast amounts of information available into one simple set of search results… We want to help you find the very best answer, even if you don't know where to look."[30]

Google search consists of a series of localized websites. The largest of those, the google.com site, is the top most-visited website in the world.[31] Some of its features include a definition link for most searches including dictionary words, the number of results you got on your search, links to other searches (e.g. for words that Google believes to be misspelled, it provides a link to the search results using its proposed spelling), and many more.

Google's search engine normally accepts queries as a simple text, and breaks up the user's text into a sequence of search terms, which will usually be words that are to occur in the results, but one can also use Boolean operators, such as: quotations marks (") for a phrase, a prefix such as "+", "-" for qualified terms (no longer valid, the '+' was removed from Google on October 19, 2011),[32] or one of several advanced operators, such as "site:". The webpages of "Google Search Basics"[33] describe each of these additional queries and options (see below:Search options). Google's Advanced Search web form gives several additional fields which may be used to qualify searches by such criteria as date of first retrieval.

Google applies query expansion to the submitted search query, transforming it into the query that will actually be used to retrieve results. As with page ranking, the exact details of the algorithm Google uses are deliberately obscure, but certainly the following transformations are among those that occur:

Term reordering: in information retrieval this is a standard technique to reduce the work involved in retrieving results. This transformation is invisible to the user, since the results ordering uses the original query order to determine relevance.

Stemming is used to increase search quality by keeping small syntactic variants of search terms.[34]

Google's homepage includes a button labeled "I'm Feeling Lucky". Prior to a change[35] in 2012, when a user typed in a search and clicked on the button the user would be taken directly to the first search result, bypassing the search engine results page. The idea was that if a user is "feeling lucky", the search engine would return the perfect match the first time without having to page through the search results. According to a study by Tom Chavez of "Rapt", this feature cost Google $110 million a year as 1% of all searches use this feature and bypass all advertising.[36]

With the introduction of Google Instant, the functionality of the button behaves differently.[37] Currently, the "I'm Feeling Lucky" button changes based on your settings and what webpage you are at. If Google Instant is turned off, the button will direct to the Google Doodles gallery. If Google Instant is turned on and a user hovers over the button, the button text will spin and land on a phrase that starts with "I'm feeling" (e.g. "I'm feeling hungry" or "I'm feeling smart"). Each phrase links to a Google service related to the associated phrase.

Google Chrome and Mozilla Firefox used Lucky Search as the default search string when the user entered a query in the location bar; this functionality was deprecated in later versions.

Besides the main search-engine feature of searching for text, Google Search has more than 22 "special features" (activated by entering any of dozens of trigger words) when searching:[10][11][39]

weather – The weather conditions, temperature, wind, humidity, and forecast,[10] for many cities, can be viewed by typing "weather" along with a city for larger cities or city and state, U.S. zip code, or city and country for smaller cities (such as: weather Lawrence, Kansas; weather Paris; weather Bremen, Germany).

stock quotes – The market data[10] for a specific company or fund can be viewed, by typing the ticker symbol (or include "stock"), such as: CSCO; MSFT; IBM stock; F stock (lists Ford Motor Co.); or AIVSX (fund). Results show inter-day changes, or 5-year graph, etc. This does not work for many stock names which are one letter long, such as Macy's (M), or are common words, such as Diamond Offshore (DO) or Majesco (COOL).

time – The current time in many cities (worldwide),[10] can be viewed by typing "time" and the name of the city (such as: time Cairo; time Pratt, KS).

sports scores – The scores and schedules, for sports teams,[10] can be displayed by typing the team name or league name into the search box.

unit conversion – Measurements can be converted,[10] by entering each phrase, such as: 10.5 cm in inches; or 90 km in miles

currency conversion – A money or currency converter can be selected,[10] by typing the names or currency codes (listed by ISO 4217): 6789 Euro in USD; 150 GBP in USD; 5000 Yen in USD; 5000 Yuan in lira (the U.S. dollar can be USD or "US$" or "$", while Canadian is CAD, etc.).

calculation results can be determined,[10] as it is calculated live, by entering a formula in numbers or words, such as: 6*77 +pi +sqrt(e^3)/888 plus 0.45. Search results for the formula are displayed after the calculation result. The caret "^" raises a number to an exponent power, and percentages are allowed ("40% of 300").[11] Following the convention used in discrete mathematics, Google's calculator evaluates 0^0 to 1.[41] The calculator also uses the unit and currency conversion functions to allow unit-aware calculations. For example, "(3 EUR/liter) / (40 miles/gallon) in USD / mile" calculates the dollar cost per mile for a 40 mpg car with gas costing 3 euros a liter. The calculator also can calculate digital storage arithmetic (the calculation of bytes). For example, putting in 400MB + 489MB + 1.5GB yields the result 2425MB, or 2.37GB. This is useful since bytes are binary (power of 2), and not decimal as regular numbers are (power of 10). Caveat: it doesn't offer arbitrary precision and is subject to floating point errors in queries like 4,000,000,000,000,000 - 3,999,999,999,999,999.[42]

numeric ranges – A set of numbers can be matched by using a double-dot between range numbers (70..73 or 90..100) to match any positive number in the range, inclusive.[11] Negative numbers are treated as using exclusion-dash to not match the number.

dictionary lookup – A definition for a word or phrase can be found,[10] by entering "define" followed by a colon and the word(s) to look up (such as, "define:philosophy")

maps – Some related maps can be displayed,[10] by typing in the name or U.S. ZIP code of a location and the word "map" (such as: New York map; Kansas map; or Paris map).

movie showtimes – Reviews or film showtimes can be listed for any movies playing nearby,[10] by typing "movies" or the name of any current film into the search box. If a specific location was saved on a previous search, the top search result will display showtimes for nearby theaters for that movie.

public data – Trends for population (or unemployment rates)[10] can be found for U.S. states and counties, by typing "population" or "unemployment rate" followed by a state or county name.

real estate and housing – Home listings in a given area can be displayed,[10] using the trigger words "housing", "home", or "real estate" followed by the name of a city or U.S. zip code.

travel data/airports – The flight status for arriving or departing U.S. flights can be displayed,[10] by typing in the name of the airline and the flight number into the search box (such as: American airlines 18). Delays at a specific airport can also be viewed (by typing the name of the city or three-letter airport code plus word "airport").

package tracking – Package mail can be tracked[10] by typing the tracking number of a Royal Mail, UPS, FedEx or USPS package directly into the search box. Results will include quick links to track the status of each shipment.

patent numbers – U.S. patents can be searched[10][39] by entering the word "patent" followed by the patent number into the search box (such as: Patent 5123123).

area code – The geographical location (for any U.S. telephone area code)[10] can be displayed by typing a three-digit area code (such as: 650).

synonym search – A search can match words similar to those specified,[10] by placing the tilde sign (~) immediately in front of a search term, such as: ~fast food.

Six degrees of Kevin Bacon - A search to find the shortest path between an arbitrary actor and veteran Hollywood character actor Kevin Bacon. Simply search using 'bacon number actorname'.

Google Goggles - using the google goggles app on your smartphone you can take a photograph of anything and get quick results for your search. If you wish to pursue more detailed search results you can click the "full results" tab and get a full blown google search of the object you photographed.

Knowledge graph - A search for things, people or places that Google knows about, such as landmarks, celebrities, cities, sports teams, buildings, geographical features, movies, celestial objects, works of art and more, and information that applies to the search term is shown in the upper right. It is rooted in public information such as Wikipedia, United States Census Bureau and the CIA World Factbook.[43]

define: – The query prefix "define:" will provide a definition[44] of the words listed after it.

stocks: – After "stocks:" the query terms are treated as stock ticker symbols[44] for lookup.

site: – Restrict the results to those websites in the given domain,[44] such as, site:www.acmeacme.com. The option "site:com" will search all domain URLs named with ".com" (no space after "site:").

intext: – Prefix to search in a webpage text, such as "intext:google search" will list pages with word "google" in the text of the page, and word "search" anywhere (no space after "intext:").

allintitle: – Only the page titles are searched[44] (not the remaining text on each webpage).

intitle: – Prefix to search in a webpage title,[44] such as "intitle:google search" will list pages with word "google" in title, and word "search" anywhere (no space after "intitle:").

allinurl: – Only the page URL address lines are searched[44] (not the text inside each webpage).

inurl: – Prefix for each word to be found in the URL;[44] others words are matched anywhere, such as "inurl:acme search" matches "acme" in a URL, but matches "search" anywhere (no space after "inurl:").

The page-display options (or query types) are:

cache: – Highlights the search-words within the cached document, such as "cache:www.google.com xxx" shows cached content with word "xxx" highlighted.

link: – The prefix "link:" will list webpages that have links to the specified webpage, such as "link:www.google.com" lists webpages linking to the Google homepage.

related: – The prefix "related:" will list webpages that are "similar" to a specified web page.

info: – The prefix "info:" will display some background information about one specified webpage, such as, info:www.google.com. Typically, the info is the first text (160 bytes, about 23 words) contained in the page, displayed in the style of a results entry (for just the 1 page as matching the search).

filetype: – results will only show files of the desired type (ex filetype:pdf will return pdf files)

... but your query looks similar to automated requests from a computer virus or spyware application. To protect our users, we can't process your request right now.

We'll restore your access as quickly as possible, so try again soon. In the meantime, if you suspect that your computer or network has been infected, you might want to run a virus checker or spyware remover to make sure that your systems are free of viruses and other spurious software.

We apologize for the inconvenience, and hope we'll see you again on Google."

The screen was first reported in 2005, and was a response to the heavy use of Google by search engine optimization companies to check on ranks of sites they were optimizing. Google says the message is triggered only by high volumes of requests from a single IP address, however the use of the "allintext" operator a few times in a period of minutes has the same effect. Google apparently uses the Google cookie as part of its determination of refusing service.[46]

In June 2009, after the death of pop superstar Michael Jackson, this message appeared to many internet users who were searching Google for news stories related to the singer, and was assumed by Google to be a DDoS attack, although many queries were submitted by legitimate searchers.

Google flags search results with the message "This site may harm your computer" if the site is known to install malicious software in the background or otherwise surreptitiously. Google does this to protect users against visiting sites that could harm their computers. For approximately 40 minutes on January 31, 2009, all search results were mistakenly classified as malware and could therefore not be clicked; instead a warning message was displayed and the user was required to enter the requested URL manually. The bug was caused by human error.[47][48][49][50] The URL of "/" (which expands to all URLs) was mistakenly added to the malware patterns file.[48][49]

On certain occasions, the logo on Google's webpage will change to a special version, known as a "Google Doodle". This is a picture, drawing, or animation that includes the logo. It is usually done for a special event or day although not all of them are well known.[51] Clicking on the Doodle links to a string of Google search results about the topic. The first was a reference to the Burning Man Festival in 1998,[52][53] and others have been produced for the birthdays of notable people like Albert Einstein, historical events like the interlocking Lego block's 50th anniversary and holidays like Valentine's Day.[54] Some Google Doodles have interactivity beyond a simple search, such as the famous "Google Pacman" version that appeared on May 21, 2010.

In August 2009, Google announced the rollout of a new search architecture, codenamed "Caffeine".[55] The new architecture was designed to return results faster and to better deal with rapidly updated information[56] from services including Facebook and Twitter.[55] Google developers noted that most users would notice little immediate change, but invited developers to test the new search in its sandbox.[57] Differences noted for their impact upon search engine optimization included heavier keyword weighting and the importance of the domain's age.[58][59] The move was interpreted in some quarters as a response to Microsoft's recent release of an upgraded version of its own search service, renamed Bing.[60] Google announced completion of Caffeine on June 8, 2010, claiming 50% fresher results due to continuous updating of its index.[61] With Caffeine, Google moved its back-end indexing system away from MapReduce and onto BigTable, the company's distributed database platform.[62] Caffeine is also based on Colossus, or GFS2,[63] an overhaul of the GFS distributed file system.[64]

During the Google I/O conference in May 2013, Google's Amit Singhal presented on the future of search, explaining that a search engine's three primary functions will need to evolve and that search will need to: 1. Answer, 2. Converse, and 3. Anticipate. As part of his keynote talk, Singhal stated, "A computer you can talk to? And it will answer everything you ask it? Little did I know, I would grow up to become the person responsible for building my dream for the entire world." Conversational search technology was then featured and Singhal introduced the term "hot-wording" to describe search without the need for an interface, whereby the user simply prompts the Google search engine by stating, "OK Google." The I/O audience was then shown a demonstration in which a user asked a question and the search engine answered back in "conversation," in addition to the presentation of results for the query.[65]

The conversational search function was incorporated into the latest version of the Chrome browser during the week beginning May 20, 2013. The "OK Google" search prompt was not included into the upgrade and users are required to click on a microphone icon that appears on the right-hand side of the search box. Google displays its answer to the user's question in the form of "cards" at the top of the search results while the information is conveyed verbally—according to one search engine writer, Google continues to work through the feature's bugs.[66]

The "Hummingbird" update was announced as part of Google's 15-year anniversary and a Guardian technology journalist described it as "the biggest change to the inner workings of the world's most popular search engine since Google's "Caffeine" update in 2010." The update was progressively introduced over the month prior to the announcement and will benefit more modern forms of search, whereby users ask Google a question rather than entering keywords into the search box.[67][68]

Searches made by search engines, including Google, leave traces. This raises concerns about privacy. In principle, if details of a user's searches are found, those with access to the information—principally state agencies responsible for law enforcement and similar matters—can make deductions about the user's activities. This has been used for the detection and prosecution of lawbreakers; for example a murderer was found and convicted after searching for terms such as "tips with killing with a baseball bat".[69]

A search may leave traces both on a computer used to make the search, and in records kept by the search provider. When using a search engine through a browser program on a computer, search terms and other information may be stored on the computer by default, unless the browser is set not to do this, or they are erased. Saved terms may be discovered on forensic analysis of the computer. An Internet Service Provider (ISP) or search engine provider (e.g., Google) may store records which relate search terms to an IP address and a time.[70] Whether such logs are kept, and access to them by law enforcement agencies, is subject to legislation in different jurisdictions and working practices; the law may mandate, prohibit, or say nothing about logging of various types of information. Some search engines, located in jurisdictions where it is not illegal, make a feature of not storing user search information.[71]

In 2012 the US Federal Trade Commission fined Google US$22.5 million for violating their agreement not to violate the privacy of users of the Apple Safari (web browser).[74] The FTC was also continuing to investigate if Google's favoring of their own services in their search results violated antitrust regulations.[75]

Google Instant, displaying a search of the term "google search", having autocompleted suggestions. The first on the list also appears in the search box itself, but the rest of the search keys which weren't written by the user appear in grey color.

The old Google Suggestion has two types of suggestions:

Displaying a list with suggestions of keywords for search.

Displaying a suggestion to complete a single word, when there is no suggestion containing the entire keywords entered by the user (cancelled).

Google Instant, a feature that displays suggested results while the user types, was introduced in the US on September 8, 2010. In concert with the Google Instant launch, Google disabled the ability of users to choose to see more than 10 search results per page. At the time of the announcement, Google expected Instant to save users 2 to 5 seconds in every search, collectively about 11 million seconds per hour.[76]Search engine marketing experts speculated that Google Instant would have a great impact on local and paid search.[77] Google Search is a turn from a static HTML page into an AJAX application.[78]

In September 2012 several sources reported that Google had removed bisexual from the list of blacklisted terms for Instant Search.[83] As of August 2013[update] the word bisexual still did not autocomplete, and LGBT activists renewed efforts to have it whitelisted.[84] As of June 2014[update] "bisexuality" (but not "bisexual") and "myleak" were found.[85]

In late June 2011, Google introduced a new look to the Google home page in order to boost the use of the Google+ social tools.[86]

One of the major changes was replacing the classic navigation bar with a black one. Google's digital creative director Chris Wiggins explains: "We're working on a project to bring you a new and improved Google experience, and over the next few months, you'll continue to see more updates to our look and feel."[87] The new navigation bar has been negatively received by a vocal minority.[88]

In November 2013, Google started testing yellow labels for advertisements displayed in search results, to improve user experience. The new labels, highlighted in yellow color, and aligned to the left of each sponsored link help users clearly differentiate between organic and sponsored results.[89]

A Google Search mobile app is available for Android and iOS devices. In addition to allowing users to perform web searches, the app implements Google Now, Google's voice recognition and intelligent personal assistant software. Google Now uses a natural language user interface to answer questions, make recommendations, and perform actions by delegating requests to a set of web services. Along with answering user-initiated queries, Google Now passively delivers information to the user that it predicts they will want, based on their search habits.[90] Google Search for Android was originally introduced in 2007, the same year the Android operating system was introduced. On January 11, 2012, Google introduced an update where they included an updated and simplified user interface, along with other improvements.[91]

There are also products available from Google that are not directly search-related. Gmail, for example, is a webmail application, but still includes search features; Google Browser Sync does not offer any search facilities, although it aims to organize your browsing time.

Also Google starts many new beta products, like Google Social Search or Google Image Swirl.

In 2007, a group of Austrian researchers observed a tendency to misuse the Google engine as a "reality interface". Ordinary users as well as journalists tend to rely on the first pages of Google search, assuming that everything not listed there is either not important or merely does not exist. The researchers say that "Google has become the main interface for our whole reality. To be precise: with the Google interface the user gets the impression that the search results imply a kind of totality. In fact, one only sees a small part of what one could see if one also integrates other research tools".[95]